I have been using Flavour Art cinnamon ceylon at 20% and have zero issues aside from my sense of taste being a little wacky with other flavors for a couple hours after I switch from the cinnamon. From what I understand, FA's cinnamon is PG (not oil) based and is water soluble. It has a delicious, potent cinnamon flavor and great TH, but even at 20% it isn't really very spicy at all. I don't use polycarbonate tanks, but I haven't noticed the
juice causing any problems or deterioration with any bottles or cartos. I was interested in trying a spicier cinnamon flavor that has the burn like the good old atomic fireball candies I loved as a kid, so I was considering testing out the different Lorann and PA cinnamon flavors, but after reading up on it, I think I will just stick to FA. It's made in Italy after all, and they know how to do food and flavors over there...